Conventionally, a magnetic sensor that utilizes a magneto-resistive element has been widely used for detecting, for example, a rotational movement of an object such as a rotor in an engine or the like. The conventional magnetic sensor usually has a bias magnet for generating a bias magnetic field that biases the magnetic field around the object of interest, and has a sensor chip including the magneto-resistive element disposed between the bias magnet and the object. The conventional magnetic sensor detects the rotational movement of the object of interest as the change in the resistance value of the magneto-resistive element that is caused in part by the rotational movement of the object of interest and in part by the bias magnetic field from the bias magnet.
FIG. 9 shows a plan view of a rotation sensor as an example of the conventional magnetic sensor. The rotation sensor is implemented as a rotation sensing device for detecting a crank angle sensor in an engine of a vehicle (Refer to Japanese Patent Document JP-A-2001-116815 and JP3102268, for example).
As shown in FIG. 9, the magnetic sensor has a sensor chip 101 that includes a magneto-resistive element MRE 1 paired with a magneto-resistive element MRE 2 to make a paired-MRE 1, and also includes a magneto-resistive element MRE 3 with a magneto-resistive element MRE 4 to make a paired-MRE 2. The sensor chip 101 faces a rotor RT that is the object of detection by using the magnetic sensor. The sensor chip 101 is integrated with a processing circuit to make an integrated circuit that is molded with a resin molding 102. More practically, the sensor chip 101 is disposed on one end of a lead frame (not shown in the figure) in the resin molding 102, and the other end of the lead frame is coupled with a power terminal T1, an output terminal T2, a ground terminal T3 and the like that extend out of the resin molding 102. In addition, a bias magnet 130 is disposed in a proximity of the sensor chip 101 for generating the bias magnetic field for the paired-MREs 1 and 2. The bias magnet 130 takes a shape of cylinder with a hollow space 131 bored therein. The hollow space 131 takes a shape of a rectangular hole, and the hole extends in a longitudinal direction in the bias magnet 130. The resin molding 102 housing the sensor chip 101 is inserted in the hole to shape the magnetic sensor.
The magnetic sensor is usually implemented for use, for example, in an engine or the like with a casing that cases the resin molding 102 together with the bias magnet 130. FIG. 10 shows an illustration of an example of the magnetic sensor having a structure described above. Like parts have like numbers in FIGS. 9 and 10.
As shown in FIG. 10, a resin housing 120 integrally shapes a sensor body with the magnetic sensor that houses the resin molding 102 and the bias magnet 130 inserted in a cap member 140 that is in a shape of cylinder with a bottom. The resin housing 120 has, for example, a flange 123 for disposition on an engine, and the flange 123 has an extension that serves as a connector 124 for connecting the magnetic sensor to wiring to external devices such as electronic control units (ECUs) or the like. The terminals T1 to T3 are electrically coupled with metal terminals 100a to 100c that are disposed in the resin housing 120 for serving as the connector 124.
The rotor RT that faces the sensor chip 101 takes, for example, a shape of a gear wheel, and rotation of the rotor RT causes change of a magnetic vector that is composed as a combination of the magnetic field of the rotating rotor RT and the magnetic field of the bias magnet 130. As a result, the change of the magnetic vector is sensed as change of the resistance value of the magneto-resistive element MRE 1 to MRE 4 in the sensor chip 101 in FIG. 9, and is outputted as a rotation detection signal. Then, the rotation detection signal is provided for the external devices such as the ECUs or the like (not shown in the figure) through various kinds of devices such as a differential amplifier, a comarator, and the output terminal T2.
In this manner, the magnetic sensor having the sensor chip 101 inserted in a through hole 131 of the bias magnet 130 that takes a shape of a hollow cylinder has an improved sensitivity beside providing compactness for its shape.
However, the magnetic sensor in the above-described structure has following problems that cannot be ignored when the sensor is implemented, for example, as the crank angle sensor in the engine.
That is, the engine usually has the rotor RT on an end of a crank shaft for the detection of the rotation angle of the rotor RT. Thus, the magnetic sensor itself is generally disposed on an edge portion of a body of the engine where a disposition space at the disposal of the magnetic sensor is relatively abundant. As a result, the accuracy of the rotation detection by the magnetic sensor directly and inevitably suffers from a de-centering about an axis of rotation, a distortion or the like of the crank shaft having the rotor RT disposed thereon due to the deflection of the crank shaft.
The rotor RT of the magnetic sensor is, in recent years, planned to be disposed, for example, at a center portion of the crank shaft where the decentering, the distortion or the like is hard to occur. However, if the disposition of the rotor RT at the hard-to-be distorted portions of the crank shaft is ever possible, the engine does not usually have plenty space for disposing the magnetic sensor at those portions due to a complicated engine structure or the like as the illustration of the example shown in FIG. 10. In other words, the disposition of the magnetic sensor having an exemplary structure shown in FIG. 10 is under severe constraints of space limitation that cannot be ignored.
Further, the space limitation that restricts the disposition of the magnetic sensor for detecting the rotation angle or the like of the moving parts with accuracy is commonly found among machine tools and similar machine having a complicated structure.